Examining the methods related to the events in Global.asax
There are 2 ‘set’ of methods that fire corresponding to the events. The first set which gets invoked on each request and the second set which does not get invoked on each request. Let us explore these methods.
Methods corresponding to events that fire on each request
Application_BeginRequest() – fired when a request for the web application comes in.
Application_AuthenticateRequest –fired just before the user credentials are authenticated. You can specify your own authentication logic over here.
Application_AuthorizeRequest() – fired on successful authentication of user’s credentials. You can use this method to give authorization rights to user.
Application_ResolveRequestCache() – fired on successful completion of an authorization request.
Application_AcquireRequestState() – fired just before the session state is retrieved for the current request.
Application_PreRequestHandlerExecute() - fired before the page framework begins before executing an event handler to handle the request.
Application_PostRequestHandlerExecute() – fired after HTTP handler has executed the request.
Application_ReleaseRequestState() – fired before current state data kept in the session collection is serialized.
Application_UpdateRequestCache() – fired before information is added to output cache of the page.
Application_EndRequest() – fired at the end of each request
Methods corresponding to events that do not fire on each request
Application_Start() – fired when the first resource is requested from the web server and the web application starts.
Session_Start() – fired when session starts on each new user requesting a page.
Application_Error() – fired when an error occurs.
Session_End() – fired when the session of a user ends.
Application_End() – fired when the web application ends.
Application_Disposed() - fired when the web application is destroyed.
Show me an example!!
Let us see an example of how to use the Global.asax to catch unhandled errors that occur at the application level.
To catch unhandled errors, do the following. Add a Global.asax file (Right click project > Add New Item > Global.asax). In the Application_Error() method, add the following code:
C#
void Application_Error(object sender, EventArgs e)
{
// Code that runs when an unhandled error occurs
Exception objErr = Server.GetLastError().GetBaseException();
string err = "Error in: " + Request.Url.ToString() +
". Error Message:" + objErr.Message.ToString();
}
VB.NET
Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
' Code that runs when an unhandled error occurs
Dim objErr As Exception = Server.GetLastError().GetBaseException()
Dim err As String = "Error in: " & Request.Url.ToString() & ". Error Message:" & objErr.Message.ToString()
End Sub
Here we make use of the Application_Error() method to capture the error using the Server.GetLastError().
Conclusion:
In this article, we learnt that Global.asax is a file used to declare application-level events and objects. The file is responsible for handling higher-level application events such as Application_Start, Application_End, Session_Start, Session_End, and so on. I would encourage you to explore the methods corresponding to the events and analyze the best possible methods to use them in your application, if needed.
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